General Motor's luxury brand sales look great from 100 yards away. Up about 38% from a year earlier for the first five months. The new sedans, ATS compact and XTS big sedan, are strong sellers.

Caddy's adding high-profile, high-price, high-profit Vsport sedans to its lineup. Those are aimed at buyers who want distinction, especially under the hood, but aren't willing go embrace the somewhat raw and expensive V-Series very-high-performance models.

And even the big, old (literally) Escalade, Caddy's version of GM's Chevrolet Tahoe and Suburban, is up a couple of percent, though that means it lags the market.

But move closer to the sales details, and you see that the SRX crossover SUV, which arguably defines Cadillac because it's the brand's best-seller in a red-hot market segment, is sinking and might pull down the brand with it.

SRX sales were off about 5% the first five months in a market up more than 7%, according to Autodata.

Even worse when contrasted with those of its ilk, a category that Autodata calls sport wagon/crossover SUV. Those as a group are up 13.8% the first five months, Autodata says.

June sales will be reported July 2 and that could signal a change. But SRX wold have to report literally unbelievable sales for June to get it back in the saddle and riding alongside the other stellar Caddies.

Cadillac says SRX still outsells key competitors, remains a strong draw for affluent families and especially women buyers, and is a hot selling in China, which is a huge market for GM.

Jack Nerad, veteran of the car business and now the man who watches the whole auto market for Kelley Blue Book's kbb.com, says SRX has two key problems:

•Foreign-brand competition

•Lack of marketing attention

"The Europeans are doing a good job," he says, citing BMW X5 and X6 crossovers, and Audi's Q7 "is kicking" as well, he says.Even the Infiniti JX 35, not a direct rival because it's a bigger, three-row, crossover, is pulling away some SRX sales, Nerad believes.

Just two years ago, Cadillac gave the SRX, a mid-size, two-row crossover, a new engine and an array of tech updates, plus new trim better aimed at likely buyers for the launch of the 2012 model. But the upgrades didn't seem to "take," and now the brand's left with the unpleasant alternative of dumping more marketing dollars into the SRX to shore up its sales, as well as the total tally for the entire brand.

"Cadillac can't put all its resources into everything. It's chosen to focus instead on other (models), which it should, so SRX is kind of left out there," says Jessica Caldwell, a top industry analyst at shopping site Edmunds.com.

Cadillac's attention in on the new-to-the-lineup ATS, a small sedan it hopes will attract the BMW 3-series crowd. And now, with the Vsport version of the XTS, you'll see some attention paid in that direction.

Plus, the fully redesigned CTS mid-size sedan is coming in the fall and that'll get a huge push. It's been a big seller in the past and the new model promises to continue that if it gets a strong start.

Why is the SRX so important to Cadillac?

"The luxury segment has become the crossover SUV segment," Nerad notes. Flop there and the whole brand loses steam.

Peculiarly, SRX is selling fairly close to sticker price, on average. Roughly $1,300 less than what it says on the sticker, according to TrueCar.com data. That means buyers aren't demanding big discounts. But as recently as February and March, it was selling for more than sticker, on average, TrueCar.com shows. So something's gone stale.

Caldwell believes that SRX will appeal to the new buyers Cadillac draws with the ATS: "A lot of natural synergies with the younger buyers. An entry luxury SUV is probably the right kind for theme." So, in her view, Caddy's marketing money going to ATS will spill over and boost SRX sales eventually.

Factory rebates and other sweeteners, such as low lease payments, always help sales, but almost always at the expense of a brand's reputation. Cadillac finally seems to have won a solid reputation as the equal of European sports models, so this could be the wrong time to erode that foundation.

Whether and how GM is able to get SRX sales growing again will make a big difference on how well the brand itself keeps its momentum.